PRESSURE-VELOCITY EQUILIBRIUM HYDRODYNAMIC MODELS

This article describes mathematical models for phase separated mixtures of materials that are in pressure and velocity equilibrium but not necessarily temperature equilibrium. General conditions for constitutive models for such mixtures that exhibit a single mixture sound speed are discussed and specific examples are described.     

Experimental demonstration of subtleties in subharmonic intermittency

Experiments on the Belousov-Zhabotinsky reaction in a well-stirred flow reactor elucidate one of the routes to chaos, subharmonic intermittency (type III intermittency). Measurements conducted as a function of two independent control parameters demonstrate how difficult it is in practice to distinguish this route to chaos from subcritical period doubling transitions with similar chaotic time signatures. Necessary criteria for the establishment of a second order (continuous) transition, such as the absence of hysteresis, are discussed in the context of one-dimensional maps.     

Thermal desorption comprehensive two-dimensional gas chromatography for in-situ measurements of organic aerosols

The complexity of organic composition and temporal variability of atmospheric aerosols presents an extreme analytical challenge. Comprehensive two-dimensional gas chromatography (GC x GC) has been used on time integrated filter samples to reveal the presence of thousands of individual organic compounds in aerosols, but without defining the temporal variability in composition ideal for providing information on source resolution and human exposure to specific pollutants. We hereby introduce a new instrument, 2D-TAG, which combines our in-situ thermal desorption aerosol GC (TAG) instrument with GC x GC allowing for dramatically improved separation of organics with automated measurements at hourly timescales.     

Development of a new consumable-free thermal modulator for comprehensive two-dimensional gas chromatography

A simple and cost-effective GC × GC modulator requiring no moving parts or consumables, hence suitable for field analysis and monitoring, was developed. The modulator was constructed from a specially designed Silcosteel^® trapping capillary, installed outside the GC oven, and coated inside with polydimethylsiloxane (PDMS) stationary phase. Dual-stage modulation was accomplished by resistively heating alternate segments of the trap with a custom-designed capacitive discharge power supply. The performance of the proposed modulator was comparable to many GC × GC systems currently in use, with the injection band widths as low as 60 ms at half height. With proper selection of the stationary phase in the trap, the modulator can be used for the analysis of complex mixtures with volatility range spanning from n-C5 to n-C40.     

The kinetics and mechanism of doped corundum structure formation in an water fluid

The kinetics and mechanism of corundum formation from hydrargillite in an water medium under sub- and supercritical conditions in the presence of manganese ions was studied. The conclusion was drawn that corundum structure formation with the insertion and uniform distribution of manganese ions occurred thanks to solid-state mobility, which appeared under the conditions of reversible dehydroxylation in the interaction of a solid matrix with an water fluid. Complex defects containing Mn²⁺, Mn³⁺, and Mn⁴⁺ ions along with hydroxyl groups and oxygen vacancies were formed when corundum was doped with manganese ions in different charge states because of redox processes in a supercritical water fluid. Corundum doped with manganese exhibited ferromagnetic properties at room temperature.     

Correlation between biological activity and energies of electronic transitions in benzodiazepines. Negative ion mass spectrometry and ultraviolet absorption spectroscopy study of some derivatives

A correlation between the energies of electronic singlet transitions in benzodiazepines and their biological activity, which was revealed earlier by means of negative ion mass spectrometry with resonance electron capture, has been verified with a UV absorption spectroscopy investigation. Also, it has been noted that the energies of electronic singlet transitions in benzodiazepines are close in value to the ionization energies of atoms Cs, Rb, K, Na, Li and Tl, the cations of which are known to play an important role in nerve cell excitation processes. Copyright 1999 John Wiley & Sons, Ltd.     

Kinetics of water vapor sorption on porous glass as a method of porometry

Equilibrium low temperature nitrogen adsorption and a new method based on the kinetics of water vapor sorption at room temperature are used for a comparative study of pore morphology of high-silica porous glass. The values of the total pore volume, the specific surfaces, the effective mesopore diameters, and the fraction of each mode in the total mesopore volume are established using both techniques. It is found that the rate of water vapor sorption at constant pressure grows in inverse ratio to the diameter of cylindrical menisci in pores. The time dependence of the volume of adsorbed water is linear, while the characteristic time of filling for each pore mode varies directly with the square of the effective pore mode diameter. The proposed new kinetic porometry technique based on analyzing water vapor adsorption kinetics at room temperature is quite simple as it requires no complicated vacuum equipment and allows the simultaneous examination of large numbers of porous material samples.     

The Influence of Acidic Treatment and Mechanical Grinding on the Structural Characteristics and Morphology of Pores in Iron-Containing Sodium-Borosilicate Porous Glasses

Colloid Journal - The method of low-temperature equilibrium nitrogen adsorption and desorption has been employed to study the porous structure and morphology of porous glass (PG) with a composition...     

Gas-phase deprotonation of arylalkylamines. A collision-induced dissociation study

The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R(1)C(6)H(4)CHR(2)CH(2)NR(3)(2) (where R(1) = H, OH, F or NO(2); R(2) = H or OH; R(3) = H or CH(3)) generated by negative chemical ionization with H(2)O and D(2)O as ionizing reagents, is discussed. The negative chemical ionization mass spectra show that, in the absence of a hydroxy group in the aromatic ring, deprotonation takes place at the benzylic position whereas the proton is lost from the OH group when present. The nitro compound forms only M(-.) ions. The CID spectra of the deprotonated molecules show that fragmentations are strongly dependent on the structural features of the molecules, namely the presence or absence of substituents in the aromatic ring or aliphatic chain. Copyright 1999 John Wiley & Sons, Ltd.